In general, methods for producing enriched gas by separating specific gas from mixed gas are commercially and mainly divided into a method using a gas separation membrane and a pressure swing adsorption (PSA) method using a pressure difference applied to adsorbent such as zeolite molecular sieve (ZMS) or carbon molecular sieve (CMS). The PSA method is a process for producing enriched gas by applying the pressure difference to the adsorbent having a selective adsorption property to specific gas. The PSA method is subdivided into a general PSA method operating under atmospheric pressure or higher, a vacuum swing adsorption (VSA) method subjected to a vacuum pressure process, and a vacuum pressure swing adsorption (VPSA) method, a combination thereof, according to an operational pressure due to the pressure difference. All the above methods are called the PSA method.
The PSA method which has been developed since 1950s is often employed to commercially produce oxygen, nitrogen, hydrogen, and the like, and is applied to an oxygen water purifier or air cleaner lately in addition to air dry and thus also applied to an oxygen concentrator in the form of small sized electric home appliances. In the case that high concentrated oxygen, nitrogen, or the like is industrially produced, adsorption beds containing the adsorbent are mostly set up in the form of a tower and operate in connection with a plurality of valves.
However, when a small oxygen concentrator is applied to medical treatment or electric home appliances, the dimensions and economical efficiency thereof should be generally considered. Therefore, the oxygen concentrator should be designed to have simple adsorption beds and valves and to be effectively combined with the other parts, contrary to an industrial concentrator. Accordingly, efforts have been made to continue simplifying the adsorption beds and peripheral devices used in the vacuum swing adsorption method at the maximum by using a minimum number of the valves and devices. In the general PSA method operating under atmospheric pressure or higher, devices for sequentially applying the pressure to the respective beds have been configured by providing a plurality of the adsorption beds and a rotary valve as a valve. Although such a method has advantages in that deviation in the concentration and flow rate is small and relatively stable production is possible, there is a limitation to minimization of the rotary valve itself as mechanism comprising a motor and a rotary plate on which channels are formed. In addition, there is a limitation to economical efficiency. Furthermore, even in the case that solenoid valves are employed in the respective adsorption beds, since the solenoid valve is generally for a high pressure of one (1) atmosphere or higher, there are disadvantages in that the higher degree of process and the precision configuration, which lead to expensive costs, are required and operational control is complicated.
FIG. 1 is a schematic view of a gas concentrator having two adsorption beds 1 and 1′ for a conventional PSA process, which is generally well known. Here, an operational process of the gas concentrator is determined according to combination of pumping means. That is, according to a vacuum pumping means 4 or a gas compressing means 8 which applies a pressure to gas, the processes will be compared. If the gas compressing means 8 is solely used, since the adsorption process by the adsorbent is determined by the pressure of the gas compressing means 8 and a pressure for a desorption process generally becomes atmospheric pressure, the general PSA process is achieved.
In addition, if the vacuum pumping means 4 and the gas compressing means 8 are simultaneously used, since the desorption pressure becomes a vacuum pressure caused from the vacuum pumping means 4, the VPSA process, which operates between the vacuum pressure and a pressure by the gas compressing means 8, is achieved. If a gas supplying means 7 which is a kind of the vacuum pumping means is combined with the vacuum pumping means 4 without using the gas compressing means 8, since the adsorbent in the adsorption beds 1 and 1′ is not subjected to a compression force, the VSA process, which operates under atmospheric pressure or lower, is achieved.
Further, if all of the gas compressing means 8, the vacuum pumping means 4, and the gas supplying means 7 are used, although the VPSA process is achieved, such a case is hardly used due to the complicated configuration and economical problems.
Furthermore, since the minimization by developing a variety of processes is applied to the adsorption beds 1 and 1′ and a valve means 2 used in the V(P)SA process which operates under a vacuum pressure contrary to the PSA method which operates under atmospheric pressure or higher as described above, the design of the adsorption beds 1 and 1′ and the valve means 2 suitable to the VSA process is required.
That is, as shown in FIG. 1, a plurality (two or more) of the adsorption beds 1 and 1′ containing the adsorbent may be used. In addition, the valve means 2 for switching channels directly connected to the adsorption beds 1 and 1′ functions to exchange the vacuum pressure applied by the vacuum pumping means 4 and the pressure of mixed gas flowing in through the filter 3 or the pressure of the gas compressing means 8, which are applied to the adsorption beds 1 and 1′, with each other.
In general, if the two adsorption beds 1 and 1′ are used, the respective adsorption beds 1 and 1′ are provided with separate solenoid valves (not shown) which are controlled. If the number of the adsorption beds 1 and 1′ is large, a rotary valve (not shown) in which the channels are formed on a rotary plate driven by means of a motor to supply mixed gas to the respective adsorption beds 1 and 1′ may be used.
As shown in FIG. 1, if the VSA process, in which the two adsorption beds 1 and 1′, the vacuum pumping means 4, and the gas supplying means 7 are used, is employed, since there is no compression force applied to the valve means 2, a pilot type solenoid valve that is generally used cannot be used, but only a direct acting type solenoid valve that is driven by a direct electric force may be used.
In addition, if a single 4-way solenoid valve is used, due to its configuration, it is impossible to control the respective adsorption beds. It may be only configured such that if the adsorption bed 1 is opened, the other adsorption bed 1′ should be closed. Therefore, a flexible process cannot be realized. In addition, since the outside should communicate with one of the adsorption beds, there is a problem of the protection of the adsorbent if additional sealing devices are not used.
Therefore, generally independent 3-way solenoid valves may be used. In such a case, the connection along with the adsorption beds 1 and 1′ is complicated and the connection between the valves of the valve means 2 is required. Accordingly, there are problems of increase in dimensions, complicatedness of assembly, and disadvantage in economical efficiency.
Furthermore, a gas separating method which is commercially used has advantages and disadvantages. In the method using the gas separation membrane, although an apparatus therefor is simple, there are disadvantages related to the environment temperature, moisture discharge, or the like. In the method using the adsorbent, although there is no problem of the moisture discharge, an apparatus therefor is complicated, and it is need to pay particular attention to usual safekeeping of the adsorbent since the adsorbent is susceptible of impurities and particularly moisture.
Therefore, in the case that the adsorbent is used, the disadvantage should be compensated for by simplifying the apparatus therefor at the maximum and the apparatus should be configured so as to be less influenced by the moisture. Although it is required to filter only up to dust by performing a preprocess well in the case that the gas separation membrane is used, adsorption of fine impurities and moisture gradually increases in the case that the adsorbent is used since the adsorbent should be recycled and then used during the process. In this respect, the V(P)SA process in which a recycling process is performed by a vacuum pressure may be advantageous as compared with the general PSA process, in point of a process.
However, if the adsorption beds are not completely isolated from the outside even in the case that the V(P)SA process is used, moisture among the air can be absorbed when the operation is stopped. In order to prevent that, moisture absorbent or the like may be used. However, since it is not a method for essentially solving the problem, additional devices for completely isolating the adsorption beds 1 and 1′ from the external air are needed. A practical PSA article has a disadvantage in that all of the adsorption beds 1 and 1′ cannot be sealed if there is no additional valve in the case that a single valve is used in order to reduce cost.
Although a plurality of general valves may be used in order to seal the adsorption beds from the external air, since such a valve means has the problems of expensive cost, complicatedness in control, and increased dimensions, a simpler apparatus has been required.